Atmospheric carbon dioxide (CO2) is the largest contributor to the carbon (C) balance in terrestrial ecosystems and the climate system, fuelling the drawdown of atmospheric CO2 in vegetation and soil on decadal to centennial time scales. Here, we used a global Earth system model (BUN-ESM) with two different CO2 datasets (i.e., uniform CO2 vs. non-uniform CO2 datasets) to simulate the responses of the net system production (NEP), particularly to the non-uniform CO2 effect under the future conditions of 2071–2100 and the present conditions of 1976–2005.